1. Field of the Invention
The present invention relates to an improvement of an endless track link which is a part of an endless track as a base carrier of a construction vehicle.
2. Description of the Related Art
FIG. 6 is a side view showing a part of an endless track (a crawler belt) in the prior art and FIG. 7 is a sectional view taken on line X-X of FIG. 6.
In FIGS. 6 and 7, an endless track 200 comprises a plurality of “pieces” (a unit of the endless track). Each piece comprises a track shoe R, a pair of links 101 connected to the track shoe R, and a pin P connecting the piece to an adjacent piece (that fits into a bushing Bu in FIGS. 6 and 7).
In FIGS. 6 and 7, a bolt B fastens a track shoe R to the endless track links 101. Also shown in a nut N engaged with the bolt B, and a reference character O represents a center axis of the pin P.
In a link 101 shown in FIG. 6, there are two window areas 50. In the endless track link 101 shown in FIGS. 6 and 7, a bolt B is inserted into a through-hole of the link 101 which a through-hole is pierced through the link 101 from a side of the track shoe R to the window area 50. A nut N is placed in the window area 50, the bolt B engages with the nut N, and thereby the track shoe R is fastened to the link 101.
FIGS. 8 and 9 show the endless track link 101, respectively. FIG. 8 shows a side view of the endless track link 101 and FIG. 9 shows a sectional view on the line X-X of FIG. 8.
In FIG. 8, on both the sides of the endless track link 101 in the longitudinal direction (at both the left end 1 and the right end 2), there are a first through-hole (on the side of the left end 1) 3 through which a pin P penetrates and a second through-hole (on the side of the right end 2) 4 through which a bushing Bu penetrates.
Referring also to FIG. 9, a counter bore 32 and a through-hole 31 are formed concentrically in the first through-hole 3 and the diameter of the through-hole 31 is set so as to be smaller than that of the counter bore 32.
As shown in FIG. 9, the endless track link 101 is configured so that, when pieces are connected to each other, the opening 42 on the lower side of the second through-hole 4 faces the counter bore 32 of the first through-hole 3 in an another link 101 being shown by the chain double-dashed line in FIG. 9 (the link of an adjacent piece). The opening 42 and 32 make a generally flat plane.
As shown in FIG. 8, two window areas 50 are formed in the region between the first through-hole 3 and the second through-hole 4.
The bottom plane of a link lower part 6 (the end face on the lower side in FIG. 8) is a plane 6a to which a track shoe R (FIGS. 6 and 7) is attached. Bolt through-holes 80 piercing through to each of the window areas 50, 50 are formed from the track shoe attaching plane 6a in a direction being perpendicular to the track shoe attaching plane 6a (in the vertical direction in FIG. 8). Each of the bolt through-holes 80 is formed by, for example, drilling.
In the case of the link 101 shown in FIGS. 6 to 11, a strut (a center pillar) 10 is formed in a region being between the two window areas 50.
In contrast, there is a link that does not have a strut (a center pillar) 10 and has only one window area.
FIG. 10 shows a window area 50 described above in reference to FIG. 8 in an enlarged manner, and FIG. 10 shows a state in which a mounting bolt B and a nut N are engaged.
The endless track link 101 is a forged product. Consequently, there is a skin of forging on a nut mounting place at the periphery on the side of the track shoe attaching plane 6a (the lower side in FIG. 10) in a window area 50, and there are bumps and dips, although it is not obviously shown in FIG. 10. In case that a nut is set on the periphery on the side of the track shoe attaching plane 6a in the window area 50 as a nut seat face 50b, where the above-mentioned bumps and dips are formed, the nut slants undesirably. The nut N does not properly engage with the bolt B, and thus, it is possible that an engagement between a link 101 and a track shoe R fails.
In the prior art, broaching is applied to a nut seat face for 50b in order to secure the nut seat face 50b, to make the nut N properly engage with the bolt B without the nut N slanting, and to fasten firmly the link 101 to the track shoe R.
However, there is a problem that a process for applying the broaching is required and thus the number of processes is undesirably increased.
FIG. 11 shows a state of assembly step in which two links on the right and left hands (links 101) being connected with a pin P and a bushing Bu are fastened to a track shoe R by means of a bolt B and a nut N.
As clearly shown in reference to FIG. 8 etc., a ratio of the area of the two window areas 50 formed in the link 101 to the whole area of the link 101 is not so large. On the other hand, as shown in FIG. 11, the track shoe R considerably protrudes toward the side of the operator M relative to the link 101.
Under such circumstances, since it is necessary to visually recognize the bolt B and the nut N, to hold the nut N in a state where the operator's arm extends fully so as to secure the nut N in a suitable position. Thus, the efficiency of the assembly step for fastening the link 101 to the track shoe R is inferior in the prior art.
Here, it is also possible to weld and fix the nut N to the link 101 instead of holding the nut N with an operator's hand.
However, in a case that a welding process is applied to the link 101 which is a heat-treated product, a welded part of the link 101 is weakened in strength, and therefore, a fatal defect may be caused in a product.
For that reason, the nut N should not be welded to the link 101.
In reference to FIG. 10, as a result of analyses carried out by the applicants, it has been found that stress concentrates at both the ends of the periphery (both on the right and left ends of the periphery 50c at the lower part of the window area 50 shown in FIG. 10) on the side of the track shoe attaching plane 6a (the lower side in FIG. 10) in a window area 50 shown in FIG. 8, namely at the portions C shown by hatching in FIG. 10.
If the link 101 can be constructed so as to reduce such stress concentrations, it is possible to reduce various dimensions and the weight of the link 101. In other words, if the link 101 can be constructed so as to reduce such stress concentrations, it is possible to further reduce the weight of the link 101 relative to an other link being applied a load which is equal to a load applied to such link 101.
At the present stage, there is not a technology by which the aforementioned stress concentration has been reduced.
In other prior art, for example, there is a track link in which the engaging tooth surface may be formed so that an acute angle is proposed (for example, refer to Patent Document 1).
However, in such prior art, since the link is constructed by combining two link elements, the number of parts increases and the aforementioned various problems cannot be solved.
Patent Document 1: Japanese Patent Laid-open No. 59-220467